This invention relates generally to electrical connectors for terminating cords and, more particularly, to so-called modular plug connectors currently being utilized in a top wall of the telephone and data communications industries as well as in other applications.
Modular plug connectors are generally used to terminate both flat and round cords. Generally, a flat cord has a multiplicity of insulated conductors arranged in a spaced linear array within an outer jacket, while a round cord has a multiplicity of insulated conductors arranged in a spiral array within an outer jacket. Various configurations of such connectors are disclosed in various patents assigned to Western Electric Company, Inc., such for example as U.S. Pat. No. 3,699,498 issued Oct. 17, 1972; U.S. Pat. No. 3,761,869 issued Sept. 25, 1983; U.S. Pat. No. 3,860,316 issued Jan. 14, 1975; and U.S. Pat. No. 3,954,320 issued May 4, 1976. Another advantageous configuration of a modular plug connector is illustrated in U.S. Pat. No. 4,211,462 issued July 8, 1980 and assigned to Stewart Stamping Corporation, the assignee of the present application. Although such connectors have been made from two housing components bonded together (see, e.g., U.S. Pat. No. 3,761,869), it appears preferable to manufacture such connectors using a so-called unipartite or integrally molded housing (see, e.g., U.S. Pat. No. 3,998,514).
A modular plug connector generally includes a housing formed of a dielectric material and which defines an internal cord receiving cavity into which the end of a cord is inserted through a cord-receiving aperture formed at one of the housing ends. The cord-receiving cavity includes a jacket-receiving portion adjacent the aperture and a communicating conductor-receiving portion into which the individual insulated conductors, from which the outer jacket has been stripped, are received. A plurality of flat contact terminals, corresponding in number to the number of conductors of the cord, are inserted into individual slots defined in the housing, each terminal being aligned with and electrically engaging a respective conductor. The conductors are generally of tinsel, stranded or solid construction while the terminals have blade-like portions which engage respective conductors in a solderless connection. The flat terminals have edges which are exposed externally of the housing for engagement with respective aligned contact elements provided in a jack socket. The cord end is secured to the connector by jacket anchoring and strain relief portions integrally hinged with the housing and movable against the cord so as to prevent separation of the connector from the cord during customer use as well as to provide strain-relief facilities for the conductors and jacket.
Modular plug connectors of the type described above are presently finding increased use in terminating cords through which digital information is transmitted. For example, modular plug connectors are finding increased use in terminating cordage used in home and office computers for connecting the computers with peripheral components, in data communication applications generally, in electronic games, in telephone communication networks and in similar digital applications.
The present invention is based on the relatively recent recognition that digital technology-based electronic equipment is a major source of electromagnetic (EMI) and radio frequency (RFI) interference, which has become a problem due to the replacement of metal housings by housings formed of plastic material.
In order to prevent or at least substantially reduce the radiation of interference from cordage used in digital-based electronic equipment and to provide at least some protection from interference radiated from extraneous equipment, such cordage has conventionally been provided with "shielding" in the form of a sheath of conductive material between the outer cord jacket and the insulated conductors, the shield sheath enclosing the conductors along their length.
The shielding can be formed of any suitable material, such as aluminum foil having a thickness of about 0.3 mils applied to treated Mylar having a thickness of about 1 mil. Sheaths formed of braided metallic material have also been used in this connection.
When shielded cordage of the type described above is terminated by modular plug connectors, a so-called "drain wire" has conventionally been electrically coupled to the shield at a region proximate to the terminated ends of the cord. The drain wires are grounded to in effect terminate the shielding so that RFI, EMI, and electrostatic electricity conducted through the shield are "drained" to thereby reduce the radiation or discharge thereof.
However, the arrangement described above is not entirely satisfactory. More particularly, it has been found that there is still a tendency for EMI and RFI to be radiated from the cordage in the region at which the modular plug connector is inserted into the jack socket possibly through the space left between the connector and the socket. The problem of leaking signals described above has become quite important and has in fact led to the recent issuance of governmental regulations specifying emission level limitations especially in connection with any electronic device that uses or generates pulses or timing signals at a rate in excess of 10,000 pulses per second. Moreover, since the sheath is a current conductor, there is a danger of an electrostatic discharge (ESD) occurring during operation of the equipment. Such ESD comprises a high voltage discharge which arcs across the contacts of the connector and has the effect of shorting the electronic circuitry when drained using the conventional arrangements described above.